Question

a mixture containing CaCO3 and CaO only. When 0.3500 g of mixture was ignited and cooled, the wt of mixture was 0.3400 g. Calculate %CaO in original mixture.

Answer 1

When heated, the CaCO3 decomposes to CaO and CO2 as follows:
CaCO3 ==> CaO(s) + CO2(g)
The CaO there initially is unchanged with the heating.
So the mixture initially weighed 0.3500 and after heating it weighed 0.3400; therefore, the CO2 lost must be 0.3500-0.3400 = ??
Convert mass CO2 to mass CaCO3. The rest of it must have been the CaO there initially.